Anticonvulsant agents using cyano dimethylphenyl benzamides

ABSTRACT

This invention provides certain 4-substituted benzamide derivatives, their pharmaceutical formulations, and their use as anticonvulsant agents.

BACKGROUND OF THE INVENTION

The several anticonvulsant drugs marketed in the United States provide significant seizure relief for only 50-75% of epileptic patients. The therapeutic effects are sometimes accompanied by serious side effects such as sedation, ataxia, psychoses, suicidal depression, gastrointestinal disturbances, gingival hyperplasia, lymphadenopathies, megaloblastic anemias, hepatotoxicity, nephropathies, hirsutism, and fetal malformations. These side effects, which range in severity from mild sedation to death from aplastic anemia, are particularly troublesome since most of the marketed anticonvulsants have very low therapeutic ratios. For example, phenytoin, one of the most widely used anticonvulsants, controls seizures in man only when plasma levels reach 10 mcg/ml. Toxic effects such as nystagmus are seen at around 20 mcg/ml, ataxia is obvious at 30 mcg/ml, and lethargy is apparent at about 40 mcg/ml. See "The Pharmacological Basis of Therapeutics" (Gilman, Goodman, and Gilman, ed., 6th Ed., MacMillan Publishing Co., Inc., New York, N.Y. (1980)), p. 455. In view of these facts, most epileptologists indicate there is definite need for more selective and less toxic anticonvulsant drugs.

SUMMARY OF THE INVENTION

This invention provides p-substituted benzamides of the formula I ##STR1## wherein R₁ is --S(O)_(p) --(C₁ -C₄ alkyl), trifluoromethyl, aminomethyl, cyano, aminocarboxy, 1-imidazolyl, or --NR₃ R₄, where R₃ and R₄ are independently C₁ -C₃ alkyl, and

R₂ is methyl, methoxy, trifluoromethyl, hydroxymethyl, or chloro; and pharmaceutically acceptable acid addition salts thereof.

This invention also provides a method for treating and preventing convulsions in mammals in need of such treatment which comprises administering to said mammal an effective amount of a compound of the formula ##STR2## wherein R₁ is hydroxy, C₁ -C₄ alkoxy, --S(O)_(p) --(C₁ -C₄ alkyl), trifluoromethyl, C₁ -C₄ alkyl, aminomethyl, cyano, aminocarboxy, 1-imidazolyl, or --NR₃ R₄, where R₃ and R₄ are independently C₁ -C₃ alkyl, and

R₂ is methyl, methoxy, trifluoromethyl, hydroxymethyl, or chloro;

and pharmaceutically acceptable acid addition salts thereof.

According to a further aspect of the present invention, there are provided pharmaceutical formulations which comprise as active ingredient a benzamide of formula II in association with a pharmaceutically acceptable carrier or diluent.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENT

The present invention relates to organic compounds that are useful for treating and preventing convulsions in mammals.

The term "C₁ -C₄ alkyl" refers to straight and branched aliphatic residues of one to four carbon atoms such as methyl, ethyl, propyl, isopropyl, t-butyl, and the like, and includes within it the term "C₁ -C₃ alkyl".

The preferred compounds of this invention are those wherein R₂ is methyl and R₁ is --NR₃ R₄.

The pharmaceutically acceptable acid addition salts of this invention can be prepared by standard methods known in the art employing those acids of sufficient acidity to form acid addition salts of those compounds wherein R₂ is --NR₃ R₄. These include salts derived from inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, hydrobromic acid, hydriodic acid, phosphorous acid and the like, as well as salts derived from organic acids such as aliphatic mono- and di-carboxylic acids, phenyl-substituted alkanoic acids, hydroxy-alkanoic and -alkanedioc acids, aromatic acids, aliphatic and aromatic sulfonic acids, etc. Such pharmaceutically acceptable salts thus include sulfate, metaphosphate, pyrophosphate, chloride, bromide, iodide, fluoride, oxalate, maleate, benzenesulfonate, toluenesulfonate, chlorobenzenesulfonate, methanesulfonate, propanesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate and the like. The Preferred salts are those derived from inorganic acids, especially hydrochloric acid.

Certain of the compounds of formula I and II can be prepared by standard acylation procedures well known in the art as summarized by the following scheme: ##STR3## wherein X is bromo, chloro, or --OH.

Although any of a number of general acylation techniques may be employed, it is preferred that an acid halide (III, X is bromo or chloro) and the aniline (IV) be reacted in a nonreactive solvent, such as tetrahydrofuran or dimethylformamide, preferably in the presence of an acid scavenger such as a carbonate, especially potassium carbonate, or an organic base, such as triethylamine or pyridine. Although it is preferred that the reactants be added in the approximate molar ratio of about 1.25:1 (III:IV), other ratios are operative. The reaction is carried out from about room temperature up to the reflux temperature of the reaction mixture. Under the preferred conditions of approximately 25° C., the reaction is generally complete in 1-2 hours.

Standard coupling techniques employing carboxylic acids (III, X=--OH) may also be employed using coupling reagents such as DCC, EEDQ, CDI, etc.

The amino substituted compounds of this invention may also be prepared from the corresponding fluoro compound (ie, a compound of general structure I or II except that R₁ is fluoro) by reacting with imidazole or an amine of the formula R₃ R₄ NH. In general, this reaction is accomplished by reacting a large excess of the amine with the fluoro intermediate, preferably in the presence of a non-reactive solvent such as dimethylsulfoxide, tetrahydrofuran, or the like. The reaction is generally carried out at temperatures from about 100°-150° C. in a sealed reaction vessel. At the preferred reaction temperature of 150° C., the reaction is generally complete within approximately 18 hours.

Other compounds of the invention may also be derived from related compounds. For example, the nitrile compounds of this invention (I, R₁ =--CN) may be transformed into the corresponding aminomethyl analogs (I, R₁ =H₂ NCH₂ --) upon catalytic hydrogenation of the nitrile. Generally, this transformation is accomplished by hydrogenating the nitrile in a nonreactive solvent, such as tetrahydrofuran, in the presence of a catalyst, for example 5% palladium on carbon, until the theoretical amount of hydrogen has been consumed.

Similarly, the nitriles can be hydrolyzed to the corresponding carboxamide compounds of this invention (I, R₁ =H₂ NCO--). The preferred method of accomplishing this transformation involves heating the nitrile at reflux in alcoholic solution of 3-4 equivalents of a strong base, such as sodium or potassium hydroxide. When employing the preferred alcohol t-butanol, the reaction is usually complete in about an hour.

The thio derivatives and intermediates of this invention (p is 0) may be transformed into the corresponding sulfoxide (p is 1) compounds upon treatment with a mild oxidizing agent, such as hydrogen peroxide in methanol, meta-chloroperbenzoic acid (MCPBA) in methylene chloride at 0° C., or an alkali metal periodate in aqueous alcohol. The corresponding sulfones (p is 2) are prepared from the thio or sulfoxide compounds on treatment with a strong oxidizing agent such as hydrogen peroxide in acetic acid or m-chloroperbenzoic acid in methylene chloride at 20°-30° C.

The hydroxy compounds (II, R₁ =OH) can be prepared from the corresponding methoxy derivatives by standard demethylation techniques. The preferred method comprises the use of boron tribromide in a nonreactive solvent such as methylene chloride as provided in Example 15 which follows.

The intermediates of Formulas II and IV and other necessary reagents for preparing the compounds employed in this invention are commercially available, are known in the art, or can be prepared by methods taught in the literature.

The p-substituted benzamides of Formula II are anticonvulsant agents and may be administered by various routes including the oral, rectal, transdermal, subcutaneous, intravenous, intramuscular, or intranasal routes, being usually employed in the form of a pharmaceutical composition. It is a special feature of these compounds that they are effective following oral administration. The invention includes a pharmaceutical composition comprising from about 1% to about 95% by weight of a p-aminobenzamide of Formula II, or a pharmaceutically acceptable acid addition salt thereof, associated with a pharmaceutically acceptable carrier.

In making the compositions of the present invention, the active ingredient will usually be mixed with a carrier, or diluted by a carrier, or enclosed within a carrier which may be in the form of a capsule, sachet, paper or other container. When the carrier serves as a diluent, it may be a solid, semi-solid or liquid material which acts as a vehicle, excipient or medium for the active ingredient. Thus, the composition can be in the form of tablets, pills, powders, lozenges, sachets, cachets, elixirs, suspensions, emulsions, solutions, syrups, aerosols (as a solid or in a liquid medium), ointments containing for example up to 10% by weight of the active compound, soft and hard gelatin capsules, suppositories, sterile injectable solutions and sterile packaged powders.

Some examples of suitable carriers and diluents include lactose, dextrose, sucrose, sorbitol, mannitol, starches, gum acacia, calcium phosphate, alginates, tragacanth, gelatin, calcium silicate, microcrystalline cellulose, polyvinylpyrrolidone, cellulose, water, syrup, methyl cellulose, methyl- and propylhydroxybenzoates, talc, magnesium stearate and mineral oil. The formulations can additionally include lubricating agents, wetting agents, emulsifying and suspending agents, preserving agents, sweetening agents or flavoring agents. The compositions of the invention may be formulated so as to provide quick, sustained or delayed release of the active ingredient after administration to the patient.

The compositions are preferably formulated in a unit dosage form, each dose containing from about 5 to 500 mg, more usually 25 to 300 mg, of the active ingredient. The term "unit dosage form" refers to physically discrete units suitable as unitary dosages for human subjects and other mammals, each unit containing a predetermined quantity of active material calculated to produce the desired therapeutic effect, in association with the required pharmaceutical carrier.

The active compounds are effective over a wide dosage range. For example, dosages per day will normally fall within the range of about 0.5 to 300 mg/kg of body weight. In the treatment of adult humans, the range of about 1 to 50 mg/kg, in single or divided doses, is preferred. However, it will be understood that the amount of the compound actually administered will be determined by a physician, in the light of the relevant circumstances including the condition to be treated, the choice of compound to be administered, the chosen route of administration, the age, weight, and response of the individual patient, and the severity of the patient's symptoms.

The following examples further illustrate the preparation of the intermediates, compounds, and formulations of this invention. The examples are illustrative only and are not intended to limit the scope of the invention in any way.

EXAMPLE 1 N-(2,6-dimethylphenyl)-4-(trifluoromethyl)benzamide

A solution of 25 g of 4-trifluoromethylbenzoyl chloride in tetrahydrofuran was added to 14.5 g of 2,6-dimethylaniline and 16.7 ml of triethylamine in tetrahydrofuran. The reaction was stirred at ambient temperature overnight, chilled, and filtered. The filtrate was evaporated in vacuo and the residue therefrom was dissolved in chloroform, washed sequentially with 1M hydrochloric acid, 1M sodium hydroxide, water, and a saturated sodium chloride solution, dried over sodium sulfate, filtered, and evaporated in vacuo. Crystallization from methanol provided the desired title product in 85% yield, m.p. 206°-207° C.

Analysis for C₁₆ H₁₄ F₃ NO: Calculated: C, 65.52; H, 4.81; N, 4.78; Found: C, 65.62; H, 4.97; N, 4.88.

EXAMPLES 2-5

The following benzamides were prepared from the appropriately substituted benzoyl chloride according to the procedure of Example 1.

2. 4-Cyano-N-(2,6-dimethylphenyl)benzamide, 67% yield, m.p. 185°-187° C.

Analysis for C₁₆ H₁₄ N₂ O: Calculated: C, 76.78; H, 5.64; N, 11.19; Found: C, 76.84; H, 5.36; N, 11.11.

3. N-(2,6-dimethylphenyl)-4-methylbenzamide, 83% yield, m.p. 163°-164° C.

Analysis for C₁₆ H₁₇ NO: Calculated: C, 80.30; H, 7.16; N, 5.85; Found: C, 80.47; H, 7.02; N, 5.69.

4. N-(2,6-dimethylphenyl)-4-methoxybenzamide, 94% yield, m.p. 168°-170° C.

Analysis for C₁₆ H₁₇ NO₂ : Calculated: C, 75.27; H, 6.71; N, 5.49; Found: C, 75.15; H, 6.58; N, 5.19.

5. N-(2,6-dimethylphenyl)-4-(methylthio)benzamide, 76% yield, m.p. 183°-185° C.

Analysis for C₁₆ H₁₇ NOS: Calculated: C, 70.81; H, 6.31; N, 5.16; S, 11.82; Found: C, 71.08; H, 6.48; N, 5.19; S, 11.99.

EXAMPLE 6 4-(Dimethylamino)-N-(2,6-dimethylphenyl)benzamide

A. Preparation of N-(2,6-dimethylphenyl)-4-fluorobenzamide.

The subtitle intermediate was prepared in 68% yield from 4-fluorobenzoyl chloride following the procedure of Example 1, m.p. 180°-181° C.

Analysis for C₁₅ H₁₄ FNO: Calculated: C, 74.06; H, 5.80; N, 5.76; Found: C, 73.83; H, 5.76; N, 5.76.

B. Preparation of 4-(dimethylamino)-N-(2,6-dimethylphenyl)benzamide.

Ten grams of N-(2,6-dimethylphenyl)-4-fluorobenzamide were dissolved in 50 ml of dimethylsulfoxide in a high pressure/temperature bomb. Anhydrous dimethylamine (18.5 g) was added and the reaction vessel sealed and heated at 150° C. for 18 hours. The bomb was cooled and the contents poured into water. The mixture was extracted with chloroform. The organic layer was washed with water and a saturated sodium chloride solution, dried over anhydrous sodium sulfate, and concentrated in vacuo. The resulting residue was crystallized from methanol/water affording the desired title product in 56% yield, m.p. 215°-217° C.

Analysis for C₁₇ H₂₀ N₂ O: Calculated: C, 76.09, H, 7.51; N, 10.44; Found: C, 75.85; H, 7.52; N, 10.15.

EXAMPLES 7-9

The following products were prepared according to the procedure of Example 6B employing the appropriate amine.

7. N-(2,6-dimethylphenyl)-4-(ethylamino)benzamide, 56% yield, m.p. 145°-147° C.

Analysis for C₁₇ H₂₀ N₂ O: Calculated: C, 76.09; H, 7.51; N, 10.44; Found: C, 75.86; H, 7.27; N, 10.14.

8. N-(2,6-dimethylphenyl)-4-(methylamino)benzamide, 35% yield, m.p. 163°-164° C.

Analysis for C₁₆ H₁₈ N₂ O: Calculated: C, 75.56; H, 7.13; N, 11.01; Found: C, 75.80; H, 7.18; N, 10.99.

9. N-(2,6-dimethylphenyl)-4-(methylpropylamino)benzamide, 49% yield, m.p. 159°-160° C.

Analysis for C₁₉ H₂₄ N₂ O: Calculated: C, 76.99; H, 8.16; N, 9.45; Found: C, 76.78; H, 7.96; N, 9.29.

EXAMPLE 10 N-(2,6-dimethylphenyl)-4-(1H-imidazol-1-yl)benzamide hydrochloride

Imidazole (3.5 g) was dissolved in a small volume of dimethylformamide and added to a slurry of 1.81 g of 60% sodium hydride in oil in dimethylformamide. Five grams of N-(2,6-dimethylphenyl)-4-fluorobenzamide in a small volume of dimethylformamide was added to the reaction mixture. The reaction was heated at 100° C. for 18 hours, cooled, and poured into water. The mixture was extracted with ethyl acetate. The organic portion was washed with water and a saturated sodium chloride solution, dried over sodium sulfate, and concentrated in vacuo. The residue was chromatographed over silica gel eluting with an ethyl acetate and hexane gradient. The solvents of the combined appropriate fractions were removed in vacuo. The hydrochloride salt was generated by adding gaseous hydrogen chloride into a solution of the residue in ethanol. Crystallization of the recovered product from ethanol/ether provided the title product in 62% yield, m.p. 259°-261° C.

Analysis for C₁₈ H₁₇ N₃ O.HCl: Calculated: C, 65.95; H, 5.53; N, 12.82; Found: C, 62.72; H, 5.34; N, 12.87.

EXAMPLE 11 4-(Aminomethyl)-N-(2,6-dimethylphenyl)benzamide hydrochloride

Ten grams of 4-cyano-N-(2,6-dimethylphenyl)benzamide were dissolved in 150 ml of tetrahydrofuran and hydrogenated over 5% palladium-on-carbon catalyst at 60 psi until the theoretical amount of hydrogen had been taken up. The catalyst was removed by filtration and the solvent evaporated in vacuo affording an oil. The oil was chromatographed over silica gel eluting with a methanol in methylene chloride gradient. The appropriate fractions were combined and concentrated in vacuo to provide a foam. The hydrochloride salt was generated by dissolving the foam in ethanol and bubbling in anhydrous hydrogen chloride gas. After evaporation, the hydrochloride salt was crystallized from ethanol affording the title product in 61% yield, m.p. 277°-279° C.

Analysis for C₁₆ H₁₈ N₂ O.HCl: Calculated: C, 66.09; H, 6.59; N, 9.63; Found: C, 65.95; H, 6.62; N, 9.71.

EXAMPLE 12 N-(2,6-Dimethylphenyl)-1,4-benzendicarboxamide

Ten grams of 4-cyano-N-(2,6-dimethylphenyl)benzamide and 3 grams of finely powdered potassium hydroxide were slurried in t-butanol and heated at reflux for 50 minutes. The homogeneous mixture was poured into a saturated sodium chloride solution and extracted in chloroform. Material which was insoluable in both the organic and water phases were recovered by filtration, crystallized from methanol, and provided the title compound in 43% yield, m.p. 246°-248° C.

Analysis for C₁₆ H₁₆ N₂ O₂ : Calculated: C, 71.62; H, 6.09; N, 10.44; Found: C, 71.33; H, 6.01; N, 10.38.

EXAMPLE 13 N-(2,6-dimethylphenyl)-4-(methylsulfinyl)benzamide

Ten grams of N-(2,6-dimethylphenyl)-4-(methylthio)benzamide were dissolved in a small volume of chloroform and chilled to 0° C. A solution of 7.9 g of m-chloroperoxybenzoic acid in chloroform was added in dropwise fashion. The reaction was stirred at room temperature for 1 hour, washed with a sodium bicarbonate solution, water, and a saturated chloride solution, dried over sodium sulfate and evaporated in vacuo. The resulting foam was chromatographed over silica gel eluting with an ethyl acetate in hexane gradient. The appropriate fractions were combined and the solvent removed in vacuo and the resulting residue was crystallized from ethyl acetate/hexane providing the desired title product in 59% yield, m.p. 144°-146° C.

Analysis for C₁₆ H₁₇ NO₂ S: Calculated: C, 66.87; H, 5.96; N, 4.87; Found: C, 67.10; H, 6.09; N, 4.77.

EXAMPLE 14 N-(2,6-dimethylphenyl)-4-(methylsulfonyl)benzamide

The title product was prepared in 86% yield following the procedure of Example 13 employing 7 g of the methylthiobenzamide and 10.6 g of m-chloroperoxybenzoic acid, m.p. 164°-165.5° C.

Analysis for C₁₆ H₁₇ NO₃ S: Calculated: C, 63.34; H, 5.65; N, 4.62; Found: C, 63.13; H, 5.71; N, 4.55.

EXAMPLE 15 N-(2,6-dimethylphenyl)-4-hydroxybenzamide

A solution of 6.4 g of N-(2,6-dimethylphenyl)-4-methoxybenzamide in methylene chloride was cooled to -75° C. Boron tribromide (25 g) was added over a 15 minute period. The reaction mixture was allowed to warm over 2 hours and then heated at reflux for 2 hours. The reaction was again cooled to -75° C. and 50 ml of water were added. The mixture was allowed to warm and the layers were separated. The organic layer was dried over sodium sulfate and evaporated in vacuo. The residue was crystallized fromm methanol/water affording the desired title product in 80% yield, m.p. 232°-234° C.

Analysis for C₁₅ H₁₅ NO₂ : Calculated: C, 74.67; H, 6.27; N, 5.81; Found: C, 74.39; H, 6.14; N, 5.58.

The following formulation examples may employ as active compounds any of the pharmaceutical compounds of the invention or their pharmaceutically acceptable salts.

EXAMPLE 16

Hard gelatin capsules are prepared using the following ingredients:

    ______________________________________                                                        Quantity (mg/capsule)                                           ______________________________________                                         4-Cyano-N--(2,6-dimethyl-                                                                       250                                                           phenyl)benzamide                                                               Starch dried     200                                                           Magnesium stearate                                                                               10                                                           ______________________________________                                    

The above ingredients are mixed and filled into hard gelatin capsules in 460 mg quantities.

EXAMPLE 17

A tablet formula is prepared using the ingredients below:

    ______________________________________                                                         Quantity (mg/tablet)                                           ______________________________________                                         4-(Dimethylamino)-N--(2,6-                                                                       250                                                          dimethylphenyl)benzamide                                                       Cellulose, microcrystalline                                                                      400                                                          Silicon dioxide, fumed                                                                            10                                                          Stearic acid       5                                                           ______________________________________                                    

The components were blended and compressed to form tablets each weighing 665 mg.

EXAMPLE 18

An aerosol solution is prepared containing the following components:

    ______________________________________                                                          Weight %                                                      ______________________________________                                         N--(2,6-dimethylphenyl)-4-                                                                         0.25                                                       methoxybenzamide                                                               Ethanol            29.75                                                       Propellant 22      70.00                                                       (Chlorodifluoromethane)                                                        ______________________________________                                    

The active compound is mixed with ethanol and the mixture added to a portion of the propellant 22, cooled to -30° C. and transferred to a filling device. The required amount is then fed to a stainless steel container and diluted with the remainder of the propellant. The valve units are then fitted to the container.

EXAMPLE 19

Tablets each containing 60 mg of active ingredient are made up as follows:

    ______________________________________                                         N--(2,6-dimethylphenyl)-4-                                                                             60     mg                                              (ethylamino)benzamide                                                          Starch                  45     mg                                              Microcrystalline cellulose                                                                             35     mg                                              Polyvinylpyrrolidone    4      mg                                              (as 10% solution in water)                                                     Sodium carboxymethyl starch                                                                            4.5    mg                                              Magnesium stearate      0.5    mg                                              Talc                    1      mg                                              Total                   150    mg                                              ______________________________________                                    

The active ingredient, starch and cellulose are passed through a No. 45 mesh U.S. sieve and mixed thoroughly. The solution of polyvinylpyrrolidone is mixed with the resultant powders which are then passed through a No. 14 mesh U.S. sieve. The granules so produced are dried at 50°-60° C. and passed through a No. 18 mesh U.S. sieve. The sodium carboxymethyl starch, magnesium stearate and talc, previously passed through a No. 60 mesh U.S. sieve, are then added to the granules which, after mixing, are compressed on a tablet machine to yield tablets each weighing 150 mg.

EXAMPLE 20

Capsules each containing 80 mg of medicament are made as follows:

    ______________________________________                                         N--(2,6-dimethylphenyl)-4-(methyl-                                                                   80 mg                                                    amino)benzamide sulfate                                                        Starch                59 mg                                                    Microcrystalline cellulose                                                                           59 mg                                                    Magnesium stearate     2 mg                                                    Total                 200 mg                                                   ______________________________________                                    

The active ingredient, cellulose, starch and magnesium stearate are blended, passed through a No. 45 mesh U.S. sieve, and filled into hard gelatin capsules in 200 mg quantities.

EXAMPLE 21

Suppositories each containing 225 mg of active ingredient are made as follows:

    ______________________________________                                         N--(2,6-dimethylphenyl)-4-                                                                            225 mg                                                  (methylpropylamino)benzamide                                                   Saturated fatty acid 2,000 mg                                                  glycerides to                                                                  ______________________________________                                    

The active ingredient is passed through a No. 60 mesh U.S. sieve and suspended in the saturated fatty acid glycerides previously melted using the minimum heat necessary. The mixture is then poured into a suppository mold of nominal 2 g capacity and allowed to cool.

EXAMPLE 22

Suspensions each containing 50 mg of medicament per 5 ml dose are made as follows:

    ______________________________________                                         N--(2,6-dimethylphenyl)-4-hydroxybenzamide                                                                50     mg                                           Sodium carboxymethyl cellulose                                                                            50     mg                                           Syrup                      1.25   ml                                           Benzoic acid solution      0.10   ml                                           Flavor                     q.v.                                                Color                      q.v.                                                Purified water to          5      ml                                           ______________________________________                                    

The medicament is passed through a No. 45 mesh U.S. sieve and mixed with the sodium carboxymethyl cellulose and syrup to form a smooth paste. The benzoic acid solution, flavor and color are diluted with some of the water and added, with stirring. Sufficient water is then added to produce the required volume.

The compounds of Formula II are anticonvulsant agents with a large therapeutic ratio and long half-life and are therefore useful in the treatment and prevention of convulsions in mammals. Moreover, the anticonvulsant compounds of this invention, in contrast to some anticonvulsant benzamides taught in the art, lack genetic toxicity and do not cause hemolysis. The compounds are effective against tonic extensor seizures elicited by maximal electroshock and should therefore be useful for treating generalized tonic-clonic ("grand mal"), cortical focal, complex partial (temporal lobe epilepsy), simple partial (focal motor), and post-traumatic seizures in humans. This activity is demonstrated in the electroshock induced convulsion inhibition assay which follows.

In the electroshock induced convulsion inhibition assay (E.S.), the compound to be tested was suspended in acacia and administered by gavage to each of ten Cox standard strain albino male mice (18-24 g) of the dose level being investigated. Thirty to 180 minutes after compound administration, the mice were subjected to a 0.1 second, 50 milliampere electroshock through corneal electrodes. The animals were examined and evaluated immediately after the electroshock for the occurrence of clonic, flexor tonic, or extensor tonic convulsions, or death and the ED₅₀ was determined for each compound as the dose which inhibited the occurrence of extensor tonic convulsions in one half of the animals immediately after the electroshock. For comparison, 18 milliamperes were usually sufficient to produce extensor tonic convulsions in about half of the control animals; at 50 milliamperes, almost all control animals (receiving vehicle only) died. The test results summarized in Table I are reported as the ED₅₀ values at the time interval found to provide an optimal response after dosing.

                  TABLE I                                                          ______________________________________                                         Anti-convulsant Activity of compounds of Formula I                                         Electroshock                                                                               Time after                                             Example No. ED.sub.50 (mg/kg)*                                                                         dosing (minutes)**                                     ______________________________________                                         1           ca.     225     60                                                 2                   13.2    60                                                 3           ca.     250     30                                                 4                   15      30                                                 5           ca.     75      180                                                6                   3.65    120                                                7                   2.45    60                                                 8                   2.0     120                                                9                   4.6     120                                                10          ca.     50      120                                                11                  38      60                                                 12          ca.     75      60                                                 13                  13      60                                                 14                  14      60                                                 15                  11.2    60                                                 ______________________________________                                          *oral dose (gavage)See text for methodology.                                   **Time (between dosing and administration of the electroshock) providing       an optimal response.                                                      

We claim:
 1. A method for treating or preventing convulsions in mammals in need of such treatment which comprises administering to said mammal an effective anti-convulsant amount of a compound of the formula ##STR4## wherein R₁ is cyano, andR₂ is methyl, methoxy, trifluoromethyl, hydroxymethyl, or chloro, or a pharmaceutically acceptable acid addition salt thereof.
 2. The method of claim 1 employing a compound wherein R₂ is methyl.
 3. An anti-convulsant pharmaceutical formulation which comprises an effective anti-convulsant amount of a compound of the formula ##STR5## wherein R₁ is cyano andR₂ is methyl, methoxy, trifluoromethyl, hydroxymethyl, or chloro or a pharmaceutically acceptable acid addition salt thereof; in association with a pharmaceutically acceptable carrier or diluent.
 4. A formulation according to claim 3 employing a compound wherein R₂ is methyl. 